Apparatus and method for edge processing of glass for light coupling

ABSTRACT

Methods and apparatus for finishing an edge of a glass sheet are described. The edge of the glass sheet is finished using two grinding wheels mounted on spindles so that the edge of the grinding wheels chamfer the edge of the glass sheet during relative movement of the grinding wheels and the glass sheet.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of priority under 35 U.S.C. § 119 of U.S. Provisional Application Ser. No. 62/490,869 filed on Apr. 27, 2017, the content of which is relied upon and incorporated herein by reference in its entirety.

TECHNICAL FIELD

Embodiments of the disclosure are directed to apparatus and methods for processing the edge of glass sheets. In particular, embodiments of the disclosure are directed to apparatus and methods for processing edges of glass sheets in increase light coupling through the glass sheet.

BACKGROUND

Glass sheets are finished by grinding and polishing an edge of the glass sheet in the manufacture of various products, for example, a light guide plate (LGP), which is used in the back-light of edge-lit liquid crystal display (LCD) device to distribute light evenly over the display panel. Side lit back light units for such devices include an LGP that is usually made of high transmission plastic materials such as polymethylmethacrylate (PMMA). The trend toward thinner displays has been limited by challenges associated with using polymer light guide plates (LGPs). Although such plastic materials present excellent properties such as light transmission, these materials have relatively poor mechanical properties such as rigidity, coefficient of thermal expansion (CTE) and moisture absorption. In particular, polymer LGPs lack the dimensional stability required for ultra-slim displays. When a polymer LGP is subjected to heat and humidity, the LGP can warp and expand, compromising the opto-mechanical performance. The instability of polymer LGPs requires designers to add a wider bezel and a thicker backlight with air gaps to compensate for this movement.

Glass sheets have been proposed as a LGP replacement solution for displays, but the glass sheets must have the appropriate attributes to achieve sufficient optical performance in terms of transmission, scattering and light coupling. Glass sheets for light guide plates must meet such edge specifications as perpendicularity, straightness and flatness. Corning Incorporated sells a Corning Iris™ glass as a replacement for PMMA and other clear plastic materials for LGPs. The Iris™ glass is exceptionally transparent, with absorption or scattering loss for the light propagating along the LGP and guided by the total internal reflection as low as 0.2 dB/m or less over the 450-650 nm visible light wavelength range. Additionally, the CTE of the glass is much lower than the CTE of suitable plastics and closer to that of the LCD display panel, making integration of a large size flat panel TV set much easier. Furthermore, the superior mechanical strength and rigidity, and the low CTE, allow for the significant reduction in thickness of the bezel of a LCD.

One of the significant requirements to a light guide plate is efficient light coupling of a light emitting diode (LED) to the light guide plate. The coupling benefits from the reduced gap between the LED and the LGP edge, and also provides the greatest surface area on the edge to allow the most light to couple through. This is different from traditional display glass processes which are focused on creating rounded edges, with diffuse surfaces, to survive failure modes with impact and chipping and other transportation related modes. Therefore, there is a need in the art for apparatus and methods to provide glass light guide plates with increased light coupling efficiency.

SUMMARY

A first aspect of the disclosure pertains to an apparatus for finishing an edge of a glass sheet by grinding the edge of the glass sheet. In one or more embodiments, such an apparatus comprises a worktable which supports the glass sheet while the edges are subjected to grinding and polishing. An X-axis is a direction of lateral movement on a plane of a glass sheet on the worktable. A Y-axis is a direction of longitudinal movement on the plane which is perpendicular to the X-axis. A Z-axis is a direction of orthogonal movement with respect to the plane. A first motor is positioned on a first side of the plane. The first motor has a first spindle with a first spindle axis of rotation aligned substantially along the X-axis. A second motor is positioned on a second side the plane. The second motor has a second spindle with a second spindle axis of rotation aligned substantially along the X-axis. A first grinding wheel is mounted on the first spindle. The first grinding wheel is substantially disc-shaped with a peripheral edge to chamfer a first edge of the glass sheet using the peripheral edge of the first grinding wheel. A second grinding wheel is mounted on the second spindle. The second grinding wheel is substantially disc-shaped with a peripheral edge to chamfer a second edge of the glass sheet using the peripheral edge of the second grinding wheel.

A second aspect of the disclosure pertains to a method to finish an edge of a glass sheet. The methods comprise supporting a glass sheet on a worktable with a portion of the glass sheet extending a distance from the worktable. The glass sheet comprises a first surface, a second surface opposing the first surface and an end surface. The first surface and end surface intersect along a first edge and the second surface and the end surface intersect along a second edge. An X-axis is a direction of lateral movement on a plane of a glass sheet on the surface. A Y-axis is a direction of longitudinal movement on the plane which is perpendicular to the X-axis. A Z-axis is a direction of movement orthogonal to the plane. The first edge is contacted with a peripheral edge of at least one substantially disc-shaped first grinding wheel positioned on a first spindle axis of a first motor. The second edge is contacted with a peripheral edge of at least one second substantially disc-shaped grinding wheel positioned on a second spindle axis of a second motor. Relative motion between the first and second grinding wheels and the glass sheet is produced during contact of the first and second grinding wheels with the first and second edges, respectively, to chamfer the first edge and second edge.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying figures, which are incorporated in and constitute a part of this specification, illustrate several aspects described below.

FIG. 1A is a schematic view of a portion of a glass sheet according to one or more embodiments of the disclosure;

FIGS. 1B and 1C are schematic view of a portion of a glass sheet after edge treatment according to one or more embodiments of the disclosure;

FIG. 2 is a side view of an apparatus for finishing an edge of a glass sheet showing two grinding wheels positioned to grind edges of the glass sheet according to one or more embodiments;

FIG. 3 is an overhead view of a glass sheet showing two grinding wheels positioned to treat the edges of the glass sheet in accordance with one or more embodiments of the disclosure;

FIG. 4 is a perspective view of an apparatus for finishing an edge of a glass sheet showing two grinding wheels in position to treat an edge of the glass sheet according to one or more embodiments;

FIG. 5 shows a side view of a grinding wheel on a spindle according to one or more embodiments;

FIG. 6A shows a side view of grinding wheels of an edge treatment apparatus in a grinding position according to one or more embodiments;

FIG. 6B shows a side view of grinding wheels of an edge treatment apparatus in a position to change the grinding wheels according to one or more embodiments;

FIG. 7 is a partial side view of a glass sheet showing a grinding wheel grinding an edge of a glass sheet;

FIG. 8 is a cross-sectional view of a glass sheet comprising a portion that extends from the fixturing device and showing the deflection that occurs when a force is applied to the end of the glass sheet;

FIG. 9 shows a schematic view of a portion of an edge finishing apparatus in accordance with one or more embodiment of the disclosure;

FIG. 10 shows a schematic view of a portion of an edge finishing apparatus in accordance with one or more embodiment of the disclosure;

FIG. 11 shows a schematic view of a portion of an edge finishing apparatus in accordance with one or more embodiment of the disclosure;

FIG. 12 shows a schematic view of an edge finishing apparatus in accordance with one or more embodiment of the disclosure;

FIG. 13 is a partial perspective view of a grinding wheel with a cooling system according to one or more embodiments;

FIG. 14 illustrates an exemplary embodiment of a light guide plate; and

FIG. 15 illustrates total internal reflection of light at two adjacent edges of a glass light guide plate.

DETAILED DESCRIPTION

Reference will now be made in detail to various embodiments, examples of which are illustrated in the accompanying examples and drawings.

In the following description, like reference characters designate like or corresponding parts throughout the several views shown in the figures. It is also understood that, unless otherwise specified, terms such as “top,” “bottom,” “outward,” “inward,” and the like are words of convenience and are not to be construed as limiting terms. In addition, whenever a group is described as comprising at least one of a group of elements and combinations thereof, it is understood that the group may comprise, consist essentially of, or consist of any number of those elements recited, either individually or in combination with each other. Similarly, whenever a group is described as consisting of at least one of a group of elements or combinations thereof, it is understood that the group may consist of any number of those elements recited, either individually or in combination with each other. Unless otherwise specified, a range of values, when recited, includes both the upper and lower limits of the range as well as any ranges therebetween. As used herein, the indefinite articles “a,” “an,” and the corresponding definite article “the” mean “at least one” or “one or more,” unless otherwise specified. It also is understood that the various features disclosed in the specification and the drawings can be used in any and all combinations.

Described herein are methods and apparatus for finishing edges of glass sheets. In specific embodiments, the glass sheets are finished by grinding and polishing to provide light guide plates which may be used in backlight units in accordance with embodiments of the present disclosure. In specific embodiments, light guide plates are provided that have similar or superior optical properties to light guide plates made from PMMA and that have much better mechanical properties such as rigidity, coefficient of thermal expansion (CTE) and dimensional stability in high moisture conditions compared to PMMA light guide plates.

Some embodiments of the disclosure provide methods and apparatus to produce minimal chamfer on glass light guide plates to enable maximum light coupling efficiency. Embodiments of the disclosure may provide LGPs that can be used with thinner glass LED. For example, a 1.5 millimeter (mm) LED may use a 2 mm thick LGPs, but a 1.0 mm LED uses a 1.1 mm thick LGP. Therefore, optimal coupling efficiency for the thinner LEDs requires a minimal chamfer on the LGP. In addition, the chamfers eliminate the cantilever curl generated during separation and enhance edge reliability by reducing the probability of failure due to sharp features. Cantilever curl occurs where portions of the top or bottom surface of the glass extend beyond the edge surface so that local areas of the top or bottom surface are not perpendicular to the edge surface. Cantilever curl can lead to chipping and breaking and areas with cantilever curl are more prone to damage on impact.

Studies have shown that there is about a 5% decrease in coupling efficiency as the chamfer thickness increases from 50 to 200 micrometers (microns, μm). Normalizing the chamfer height to thickness shows that the coupling efficiency remains consistent across thicknesses. However, as glass gets thinner and the LED thickness is equal to the glass thickness, the coupling efficiency is more sensitive to the LED to LGP gap for a given chamfer height/thickness ratio.

Thin glass sheets supplied to equipment manufacturers such as electronic display manufacturers typically comprise processed edges. That is, the edges are ground and shaped (e.g. chamfered) to eliminate sharp edges that are easily damaged and edge flaws (chips, cracks, etc.) resulting from the cutting process that can decrease the strength of the glass. Such plates are typically equal to or less than about 2 mm in thickness between the opposing major surfaces of the plate, and more preferably a thickness equal to or less than about 0.7 mm and in some applications a thickness equal to or less than about 0.5 mm. Very thin plates of glass can be equal to or less than 0.3 mm and still be afforded the benefits of the present disclosure.

It is known that the fracture of glass can be traced to an initial flaw, for example a small crack, and the fracture extends from this initial flaw. Fracture can occur over a very short period of time, or incrementally over an extended period of time depending on the stresses present in the article. Nevertheless, each fracture began at a flaw, and flaws are most typically found along the edge of a glass sheet, and most especially an edge that has been previously scored and cut. To eliminate edge flaws, the plate edges may be ground or polished so that only the smallest flaws remain, thereby increasing the strength of the sheet by increasing the stress necessary to propagate a flaw.

Additionally, the grinding process itself is rarely uniform, as the abrasive wheel may have a certain play or variation in its position as it traverses the glass edges. That is, the abrasive wheel may move closer to or farther from the glass sheet so that the force exerted against the plate by the grinding wheel may vary both as a function of time and/or position. This positional variation may lead to changes in the amount of material removed from an edge. The variation can result in uneven grinding and changes in the amount of particulate produced. More simply, the chamfer width may vary, and this variation is most acute if the plate edge undergoing grinding is rigid.

Referring to FIGS. 1A through 1C illustrate an exemplary end portion of a glass sheet 30 before and after edge finishing. FIG. 1A shows the glass sheet 30 before edge finishing. The glass sheet 30 includes a first surface 31, a second surface 32 that is opposing the first surface 31 and an end surface 33. The first surface 31 and end surface 33 intersect along first edge 43 and the second surface 32 and end surface 33 intersect along edge 44.

FIGS. 1B and 1C show the glass sheet 30 after edge finishing. Here, edges 43, 44 have been chamfered, providing a first chamfer 41 and a second chamfer 42. The first surface 31 intersects the first chamfer 41 at edge 46, the end surface 33 and first chamfer 41 intersect at edge 47, the end surface 33 and second chamfer 42 intersect at edge 48, and the second chamfer 42 intersects the second surface 32 at edge 49. The total thickness T_(g) of the glass sheet 30 comprises the sum of the thickness T_(C1) of the first chamfer 41, the thickness T_(e) of the end surface 33 and the thickness T_(C2) of the second chamfer 42.

The combined thickness T_(C1) of the first chamfer 41 and the thickness T_(C2) of the second chamfer 42 of some embodiments is less than about 10% of the total thickness T_(g) of the glass sheet 30. In some embodiments, the sum of the thickness T_(C1) and T_(C2) of the chamfers 41, 42 is less than about 5% of the total thickness T_(g) of the glass sheet 30. In some embodiments, the sum of the average thickness T_(C1) and T_(C2) of the chamfers 41, 42 is less than about 4%, 3%, 2.5%, 2%, 1.5% or 1% of the total thickness T_(g) of the glass sheet 30. In some embodiments, the chamfer has an average 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm or 90 μm. In some embodiments, the chamfer has an average thickness in the range of about 20 to about 80 μm, or in the range of about 20 to about 50 μm, or in the range of about 40 to about 80 μm.

The amount of particulate generated during grinding of first chamfer 41 and second chamfer 42, characterized by the chamfer widths W_(C1) and W_(C2), respectively, should be minimized. The chamfer width is defined as the length of the chamfered surface from the edge surface 33 of the glass sheet 30 to the first surface 31 or second surface 32, depending on which chamfer is being measured.

Once chamfers have been produced on the glass sheet, the resulting additional edges 46, 47, 48, 49 may be further polished to eliminate the sharp corner at those edges and form arcuate edges. This may be accomplished, for example, with a buffing wheel and suitable abrasive paste.

Shown in FIGS. 2 through 4 is an embodiment of an apparatus 100 for processing a thin glass sheet 30. FIG. 2 shows a side view, FIG. 3 shows a top view and FIG. 4 shows a perspective view of similar apparatus 100. The apparatus 100 comprises a worktable 116 which may also be referred to as a support surface. The X-axis is a direction of lateral movement of the worktable 116 and/or the grinding wheels during edge processing. The Y-axis is a direction of longitudinal movement perpendicular to the X-axis. The plane of the worktable 116 is within the X-Y plane formed by the X-axis and Y-axis. The Z-axis is orthogonal with respect to the plane of the worktable 116. While alternate configurations are possible, the embodiments illustrated provide a worktable 116 that supports a glass sheet 30 horizontally in the X-Y plane. In some embodiments, the worktable 116 supports the glass sheet 30 in a vertical orientation and moves either upward or downward.

The apparatus 100 includes a first motor 120 with a first spindle 121. The first spindle 121 is oriented so that the axis of rotation 122 is aligned substantially along the X-axis. The first spindle 121 is positioned on a first side of the plane of the worktable 116. A second motor 130 includes a second spindle 131 that is oriented so that the axis of rotation 132 is aligned substantially along the X-axis. The second spindle 131 is positioned on a second side of the plane of the worktable 116. The second side of the plane of the worktable 116 is opposite the first side of the plane of the worktable 116. For example, if the plane of the worktable 116 was oriented horizontally, the first spindle 121 might be located above the plane and the second spindle 131 might be located below the plane. As used in this manner, the term “substantially along the X-axis” means that the axis of rotation is within ±20°, ±10°, ±5°, ±4°, ±3°, ±2° or ±1° of the X-axis.

Apparatus 100 comprises a support 110 (shown in FIG. 4) that can hold and/or move the first motor 120 and/or the second motor 130. The support 110 can move the motors independently or together. In some embodiments, the first motor 120 is on a first support 110 a and the second motor 130 is on a second support 110 b, as illustrated in FIGS. 6A and 6B. The support 110 can include a Z-axis motor (not shown) to move the first motor 120 or second motor 130 in a direction perpendicular to the major plane formed by the glass sheet 30.

A first grinding wheel 125 is connected to the first spindle 121 and is rotated about the axis of rotation 122 of the spindle 121. The grinding wheels can be connected to the spindles by any suitable components as will be understood by the skilled artisan. A second grinding wheel 135 is connected to the second spindle 131 and is rotated about the axis of rotation 132 of the spindle 131. The grinding wheels can be mounted on the end of the spindle or along the length of the spindle.

The first grinding wheel 125 and the second grinding wheel 135 can be the same type of abrasive wheel or can be different. In some embodiments, the first grinding wheel 125 and the second grinding wheel 135 are compliant urethane based wheels. A urethane-based wheel has an abrasive element held together in a cross-linked urethane binder (e.g., industrial diamond held in polyurethane matrix). In some embodiments, the urethane-based wheel has a hardness on the Shore A scale (ASTM D2240) in the range of about 80 to about 104, or in the range of about 84 to about 98. An exemplary grinding wheel 125 is illustrated in FIG. 5. The grinding wheel 125 can be a substantially disc-shaped component with an inner face 126, an outer face 127 and a peripheral edge 128. As used in this manner, the term “substantially disc-shaped” means that the grinding wheel has a general appearance of a disc or drum shaped component with at least one face and a peripheral edge. The term inner face 126 refers to the face of the wheel 125 that is closer to the motor. The peripheral edge 128 provides the abrasive surface that contacts the glass sheet 30 during chamfering. The grinding wheels are aligned to rotate about the X-axis to chamfer the edge of the glass sheet 30 using the peripheral edge 128. In some embodiments, the grinding wheel uses the edge of a circular wheel including a recessed center region, generally referred to as “cup” wheels based on the cup-like shape of the abrasive wheel.

Typically, the grinding surface of the peripheral edge 128 comprises diamond particulate as a cutting medium dispersed in a suitable matrix or binder (e.g. resin or metal bond matrixes). Other cutting mediums may also be used, such as carbide particulate. The grinding wheel of some embodiments has an abrasive material with an average particle size in the range of about 200 μm to about 3 μm, or in the range of about 150 μm to about 4 μm, or in the range of about 120 μm to about 5 μm, or in the range of about 100 μm to about 6 μm, or in the range of about 60 μm to about 7 μm, or in the range of about 50 μm to about 8 μm, or in the range of about 25 μm to about 10 μm. In some embodiments, the grinding wheel has a grit in the range of about P120 to about P6000, or in the range of about P180 to about P3000, or in the range of about P240 to about P2500, or in the range of about P360 to about P2000, or in the range of about P600 to about P1500, or in the range of about P800 to about P1200, on the FEPA standard.

Referring again to FIG. 2, the glass sheet 30 supported by worktable 116 such that a portion 26 of glass sheet 30 extends beyond the worktable 116. For example, the glass sheet 30 may be positioned in a horizontal arrangement as shown, wherein the glass sheet 30 may be said to be cantilevered from the worktable 116 (also referred to as a support member or support surface). However, glass sheet 30 may be fixtured in any orientation, at any angle. For example, glass sheet 30 may be supported in a vertical orientation. Apparatus 100 may further comprise clamping member 117 comprising a rail, fingers, hooks or other suitable clamping members to secure glass sheet 30 to worktable 116. Another method of securing the plate is by including a vacuum chuck into the worktable 116 that holds the glass sheet stationary. A vacuum may be used alone or in combination with one or more clamping members. Generally, any suitable method of securing glass sheet 30 to worktable 116 may be used as long as a portion 26 of the glass sheet 30 is positioned to extend from the fixture. In some embodiments, the extending portion 26 is able to flex relative to the fixture while the glass sheet 30 is firmly attached. The glass sheet 30 may be secured to the fixture such that extending portion 26 extends a pre-determined distance L from the fixture.

Referring to FIG. 7, the grinding wheels 125, 135 contact the glass sheet 30 to chamfer the edges. The round portion of the grinding wheel may leave a slightly rounded chamfer that corresponds to the shape of the grinding wheel. However, the amount of contact of the glass sheet 30 with the grinding wheel is small enough that the chamfer appears flat, or that sufficient heat from friction causes the freshly chamfered edge to flatten. The embodiment shown in FIG. 7 is exaggerated to illustrate the angle of the chamber (measured based on the edges of the chamfer) relative to the end surface 33. The first grinding wheel 125 may form a first chamfer 41 with a first angle α relative to end surface 33. The second grinding wheel 135 is positioned so that the grinding surface of the second grinding wheel forms a second angle relative to end surface 33. The first and second angles α, β can be the substantially the same or different angles.

With reference to FIG. 2, which illustrates an embodiment of the apparatus and method in which the glass sheet 30 is moving out of the plane of the page, and FIG. 7, the first grinding wheel 125 is rotated about axis of rotation 122 and acts on first surface 31 with a force F1. This force F1 in turn may produce a deflection δ1 in glass sheet 30. That is, glass sheet 30 bends in response to the applied force. This can be seen generically with the aid of FIG. 8, showing a force F applied to glass sheet 30, thereby eliciting a response in the form of a deflection δ. The amount of bending, or compliance (the magnitude of 6), is a function of many variables, including material properties of the glass (e.g. Young's modulus) the amount of extension from the fixture, and the magnitude of the force. These variables can be lumped, and characterized by a stiffness value k, where stiffness is equal to the applied force divided by the resulting magnitude of deflection. The stiffness k can be expressed in general as

$k = {\frac{F}{\delta} \propto \frac{EI}{L^{3}}}$

where force F divided by deflection δ is also proportional to the elastic modulus E of the glass sheet multiplied by the moment of inertia I and divided by the amount of extension L of the glass sheet beyond the fixture to the third power.

It can also be shown that the amount of material removed by an abrasive wheel is directly proportional to the applied force. From the above equation it can be seen that a plate fully supported by a rigid support, with no extended portion and no deflection in a plane of the glass sheet in the presence of an applied force, the stiffness is infinite. In this instance, an increase in force, such as the force applied by an abrasive wheel on a glass sheet, will result in a commensurate increase in the amount of material removed, and therefore an increase in the chamfer width. Such a system becomes unattractively sensitive to small variations in the position of the grinding wheel as are often observed in a real life system. This sensitivity can be as high as 1:1, wherein a doubling in the applied force results in a doubling of the material removed.

On the other hand, the relationship above also suggests that if a portion of the plate is extended past the fixture (e.g. beyond worktable 116), the stiffness of the extended portion is reduced and finite and the plate may flex. For a low, finite stiffness, this compliance results in a reduced chamfer width. In other words, the deflection resulting from small positional variations of an abrasive wheel in contact with a plate having low stiffness (exhibiting compliance) can avoid large increases in material removed when compared to the same positional movement relative to a rigid plate (e.g. high stiffness). Additionally, the precision level of the chamfering apparatus need not be as high as would be necessary if the glass sheet did not exhibit compliance. This may reduce equipment costs, since, for example, bearing precision may be relaxed.

It will be understood by one skilled in the art that a similar set of circumstances can be depicted for second grinding wheel 130. That is, considering second abrasive wheel 28 b in contact with second edge 44 and applying a force F2. However, since F2 is applied in a direction opposite that for F1, displacement of the extended portion of the glass sheet 30 occurs in a direction opposite to the deflection produced by the first grinding wheel 120.

In accordance with embodiments of the present disclosure, a plurality of grinding wheels are used to produce a chamfer or chamfer on both edges of an end of a glass sheet constrained by a fixturing device and wherein the glass sheet includes a portion thereof that extends beyond the fixturing device. At least two abrasive wheels are deployed, and arranged so that each of the at least two abrasive wheels engage an end of the glass sheet on opposite sides of the glass sheet. Each wheel is rotated about an axis of rotation and relative movement along the end of the glass sheet so that double chamfers are formed along the end of the glass sheet.

For example, a chamfer 41 is formed by first grinding wheel 120 along first edge 43 of glass sheet 30. The angle α of the chamfer relative to the plane of end surface 33 in some embodiments is in the range of about 20 to about 75 degrees, or in the range of about 30 to about 70 degrees, or in the range of about 40 to about 65 degrees, or in the range of about 45 to about 65 degrees, or in the range of about 50 to about 65 degrees, or about 60 degrees. The second grinding wheel 130 similarly produces a second chamfer 42 at second edge 44. In some embodiments, the chamfer angle β is in the range of about 20 to about 75 degrees, or in the range of about 30 to about 70 degrees, or in the range of about 40 to about 65 degrees, or in the range of about 45 to about 65 degrees, or in the range of about 50 to about 65 degrees, or about 60 degrees.

To isolate the effects of the grinding wheels 120, 130, the grinding wheels 120, 130 are spaced apart a pre-determined distance D_(e) as depicted in FIG. 9. The magnitude of this pre-determined distance is selected so that the force applied by one wheel against glass sheet 30 does not influence the action of the other wheel. That is, the deflection from a plane of the glass sheet produced by one cup wheel does not cause a deflection in the glass sheet within the region of influence of other cup wheel. Put perhaps more simply still, the deflection from a plane of the glass sheet produced by one abrasive wheel does not overlap the deflection produced by the other abrasive wheel. In some embodiments, the adjacent faces of the grinding wheels are at least about 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm or 10 mm apart.

Referring again to FIGS. 6A and 6B, the first motor 120 and/or the second motor 130 may be movable in the Z-axis to move the motor, spindle and connected grinding wheel closer to or further from each other and the worktable. The Z-axis movement allows for the grinding wheels 125, 135 to be replaced and to apply a controllable amount of force to the glass sheet 30. In some embodiments, the first motor 120 and/or the second motor 130 are movable in the Z-axis by a distance equal to or greater than about 30 mm, 40 mm, 50 mm, 60 mm, 70 mm or 80 mm away from the worktable. FIG. 6A shows an embodiment in which the first motor 120 is mounted on a separate support 110 a than the second motor 130 support 110 b. The motors 120, 130 are in a processing position in which a glass sheet passing the grinding wheels 125, 135 would be edge treated. FIG. 6B shows the apparatus where the motors 120, 130, spindles 121, 131 and grinding wheels 125, 135 are moved in the Z-axis away from the processing position.

The first motor 120 and the second motor 130 can be configured to operate at any suitable speed. In some embodiments, the motors are configured to operate at a speed in the range of about 600 rpm to about 3000 rpm, or in the range of about 800 rpm to about 2500 rpm, or in the range of about 1000 rpm to about 2400 rpm, or in the range of about 1500 rpm to about 2200 rpm.

Referring to FIG. 9, the first spindle 121 and the second spindle 131 are spaced apart a distance D_(a) sufficient to prevent the first grinding wheel 125 from contacting the second spindle 131 or the second grinding wheel 135 from contacting the first spindle 121. In some embodiments, the first spindle 121 and the second spindle 131 are spaced apart by an amount greater than or equal to the radius r₁ of the first grinding wheel 125 or the radius r₂ of the second grinding wheel 135, whichever is larger, plus a safety margin. In some embodiments, the safety margin is greater than or equal to about 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, 10 mm, 11 mm, 12 mm, 13 mm, 14 mm or 15 mm. Additionally, the distance D_(c) between the centers of thickness of the grinding wheels is sufficient to prevent the adjacent faces of the grinding wheels from contacting.

The dimensions of the individual grinding wheels can vary. In some embodiments, the grinding wheels have a radius in the range of about 25 mm to about 250 mm, or in the range of about 50 mm to about 200 mm, or in the range of about 75 mm to about 150 mm, or about 100 mm, or about 150 mm or about 200 mm.

FIG. 9 shows an embodiment in which each spindle 121, 131 has a single grinding wheel 125, 135. The spindles 121, 131 are shown with approximately the same length; however, it will be understood that the length of the spindles 121, 131 can be different and the location of the grinding wheels 125, 135 on the spindles 121, 131 can be controlled to prevent contact between the grinding wheels.

In some embodiments, the first spindle 121 and/or the second spindle 131 further comprises an additional grinding wheel. FIG. 10 illustrates an embodiment in which the first spindle 121 has a single grinding wheel 125 and the second spindle 131 has two grinding wheels 135 a, 135 b. The grinding wheels 135 a, 135 b are spaced along the length of the second spindle 131 so that the grinding wheel 125 on the first spindle 121 is between the grinding wheels 135 a, 135 b. FIG. 11 illustrates another embodiment in which the first spindle 121 has two grinding wheels 125 a, 125 b and the second spindle 131 has two grinding wheels 135 a, 135 b. The grinding wheels 125 a, 125 b are spaced along the length of the first spindle 121 and the grinding wheels 135 a, 135 b are spaced along the length of the second spindle 131 so that the grinding wheels on the spindles alternate so that at least one of the grinding wheels 125 a, 125 b is between grinding wheels 135 a, 135 b and at least one of the grinding wheels 135 a, 135 b is between grinding wheels 125 a, 125 b.

The width of the grinding wheels can vary to provide a sufficient contact length with the glass sheet. In the embodiment of FIG. 9, the width W_(W1) of the grinding wheel 125 and the width W_(W2) of grinding wheel 135 are each greater than or equal to about 25 mm, 28 mm, 30 mm, 35 mm, 40 mm, 45 mm, or 50 mm. In the embodiment of FIG. 10, the width W_(W1) of the grinding wheel 125 is greater than or equal to about 25 mm, 28 mm, 30 mm, 35 mm, 40 mm, 45 mm, or 50 mm, and the combined width W_(W2a) of grinding wheel 135 a and the width W_(W2b) of grinding wheel 135 b is greater than or equal to about 25 mm, 28 mm, 30 mm, 35 mm, 40 mm, 45 mm, or 50 mm. A wheel with a larger contact length would use less force per unit area than an otherwise identical wheel with a smaller contact length.

FIG. 12 shows a schematic representation of an apparatus 100 in accordance with one or more embodiments of the disclosure. The grinding wheel 125 is connected to first spindle 121 and first motor 120 and the grinding wheel 135 is connected to the second spindle 131 and second motor 130. Each of the first motor 120 and the second motor 130 are coupled to a controller 145 using a first force transducer 147 and a second force transducer 148, respectively. A force transducer is a component that converts force into an electrical signal. For example, an exemplary force transducer has an electrical output range of 4 to 20 mA, which equates to a force range of 0 to 100N.)—match load to a transducer range. The force transducers 147, 148 can be any suitable force transducer that is capable of measuring forces in the predetermined range. The force transducer of some embodiments is operably connected to an air bearing to provide a controlled amount of force to the motor 120, 130 to produce a controlled amount of force per unit area on the glass sheet 30 by the grinding wheels 125, 135. In use, the force transducer measures the force of the grinding wheel on the glass and a feedback circuit can adjust an air bearing (or other force delivery system) to apply the desired force. Stated differently, the first motor 120 and the second motor 130 are pushed toward the surface of the worktable 116, so that if the motor were above the surface of the worktable, the motor would be pushed downward by the force transducer. The force transducer in conjunction with the controller 145 provides a feedback system that can compensate for the compliance of the individual grinding wheels so that grinding wheels with different core materials can be used. The controller 145 can be any suitable controller, microcontroller or computer and may include, for example, circuits, a central processing unit, a display unit and/or an input/output unit. In some embodiments, the force transducer is configured to maintain a pressure of the grinding wheel against the glass of about 10 N, 20 N, 30 N, 40 N or 50 N, or in the range of about 5 Newtons to about 75 Newtons, or in the range of about 10 Newtons to about 50 Newtons.

The worktable 116, or a suitable component that is coupled to the worktable, can be configured to move the glass sheet 30 at any suitable speed across the grinding wheels. As used in this manner, the term “across the grinding wheels” does not imply a direction or physical orientation of the components. Rather, the term is used to refer to the relative movement of the grinding wheels with respect to the glass sheet so that the edge of the glass sheet becomes chamfered by the grinding wheels. The worktable 116 can be configured to move the glass sheet at a rate greater than or equal to about 5 m/min, 10 m/min, 15 m/min, 20 m/min, 25 m/min or 30 m/min. In some embodiments, the worktable 116 is configured to move the glass sheet at a rate in the range of about 5 m/min to about 30 m/min.

FIG. 13 illustrates an embodiment of the apparatus 100 including a cooling system 170 to prevent overheating of the glass sheet 30 or the grinding wheel. The first motor 120, first spindle 121 and grinding wheel 125 are illustrated but it will be understood that there can be two motors, spindles or multiple grinding wheels. A single cooling system 170 can be used to cool multiple motors, spindles and/or grinding wheels or each motor, spindle and/or grinding wheel can have a separate cooling system. The cooling system 170 can include a plurality of first peripheral liquid cooling nozzles 171 adjacent the first spindle 121. The plurality of first peripheral liquid cooling nozzles 171 can be aligned or positioned to direct a cooling liquid toward the peripheral edge 128 of the grinding wheel 125 and/or toward the glass sheet. In some embodiments, the apparatus 100 includes a plurality of second peripheral liquid cooling nozzles adjacent the second spindle and positioned to direct cooling liquid toward the peripheral edge of the second grinding wheel and/or toward the edge of the glass sheet. The plurality of first peripheral liquid cooling nozzles and plurality of second peripheral cooling nozzles can share a single cooling system 170, or each of the pluralities can have a separate independent cooling system.

In one or more embodiments, the cooling nozzles are positioned a distance in a range of about 10 cm to about 200 cm, or in the range of about 40 cm to about 200 cm, or in the range of about 80 cm to about 200 cm, or in the range of about 100 cm to about 200 cm, or in the range of about 150 cm to about 200 cm from the edge of the glass sheet and/or the peripheral edge 128 of the grinding wheel 125. Cooling liquid can be flowed to remote liquid cooling nozzles 171 by liquid coolant lines 172. The cooling system 170 can be supplied by a supply line (not shown), which may be connected to a coolant source (not shown) such as a faucet supplying tap water or a pump connected to a tank (not show) containing deionized and/or demineralized water.

In one or more embodiments, the cooling system 170 is configured to be activated during chamfering of the glass sheet. The plurality of peripheral liquid cooling nozzles can include any suitable number of nozzles to provide sufficient cooling during grinding and/or polishing. The embodiment illustrated in FIG. 13 has two nozzles 171 but those skilled in the art will understand that more or less can be used. For example, three, four, five, six, seven, eight, nine, ten, eleven or twelve peripheral liquid cooling nozzles can be provided. Likewise, the plurality of second peripheral liquid cooling nozzles can include any suitable number of nozzles to provide sufficient cooling during grinding.

The remote liquid cooling nozzles 171 can be spaced at any appropriate distance from the edge of the glass sheet 30 or peripheral edge 128 of the grinding wheel 125 during chamfering. The remote liquid cooling nozzles 171 can be spaced 5 cm, 10 cm, 15 cm, 20 cm, 25 cm, 30 cm, 35 cm, 40 cm, 50, cm, 60 cm, 70 cm, 80 cm, 90 cm, 100 cm, 125 cm, 150 cm, 200 cm or up to 500 cm away from the edge of the glass sheet or the peripheral edge 128 of the grinding wheel 125 during operation.

Each of the cooling nozzles 171 can be sized and shaped as needed to obtain the desired cooling effect. For example, the openings of the cooling nozzles 171 can be 0.2 mm, 0.3 mm, 0.4 mm, 0.5 mm, 0.6 mm, 0.8 mm, 0.9 mm, 1 mm, 2 mm, 3 mm, 4 mm, 5 mm or to 10 mm in diameter. Conventional polyvinyl chloride (PVC) or other plastic tubing or metal tubing can be used for each of the coolant lines 172 and the supply lines. The cooling liquid may comprise water, chilled water or other cooling liquid.

As indicated above, the apparatus and methods described herein can be utilized in the manufacture of glass light guide plates. FIG. 14 illustrates an exemplary embodiment of a light guide plate 200 that can be made by the methods and apparatus of the present disclosure to finish a glass sheet by grinding and polishing an edge. The glass sheet has the shape and structure of a typical light guide plate comprising a glass sheet having a first face 210, which may be a front face, and a second face opposite the first face, which may be a back face. The first and second faces have a height, H, and a width, W. In one or more embodiments, the first and/or second face(s) have an average roughness (Ra) that is less than 0.6 μm, 0.4 μm or 0.2 μm, measured by a 3D optical profilometer or surface topography devices.

The glass sheet 200 has a thickness, T, between the front face and the back face, wherein the thickness forms four edges. The thickness of the glass sheet is typically less than the height and width of the front and back faces. In various embodiments, the thickness of the light guide plate is less than 1.5% of the height of the front and/or back face. In one or more embodiments, the thickness, T, may be about 2 mm, about 1.9 mm, about 1.8 mm, about 1.7 mm, about 1.6 mm, about 1.5 mm, about 1.4 mm, about 1.3 mm, about 1.2 mm, about 1.1 mm, about 1 mm, about 0.9 mm, about 0.8 mm, about 0.7 mm, about 0.6 mm, about 0.5 mm, about 0.4 mm or about 0.3 mm. In some embodiments, the thickness T of the light guide plate is in the range of about 0.1 mm to about 2.5 mm, or in the range of about 0.2 mm to about 2 mm, or in the range of about 0.3 mm to about 1.5 mm. The height, width, and thickness of the light guide plate of some embodiments are configured and dimensioned for use as a LGP in an LCD backlight application.

In the embodiment shown, a first edge 230 is a light injection edge that receives light provided, for example, by one or more light emitting diodes (LEDs). In some embodiments, the light injection edge scatters light within an angle less than 12.8 degrees full width half maximum (FWHM) in transmission. The light injection edge can be obtained by grinding and polishing the first edge 230 in accordance with apparatus and methods described herein.

The glass sheet further comprises a second edge 240 adjacent to the first edge 230 (the light injection edge) and a third edge 260 opposite the second edge 240 and adjacent to the light injection edge 230, wherein the second edge 240 and/or the third edge 260 scatter light within an angle of less than 12.8 degrees full width half maximum (FWHM) in reflection. The second edge 240 and/or the third edge 260 may comprise a diffusion angle in reflection that is less than 6.4 degrees. The glass sheet includes a fourth edge 250 opposite the first edge 230.

According to one or more embodiments, three of the four edges of the LGP have a mirror polished surface for at least two reasons: LED coupling and total internal reflection (TIR) at two edges. According to one or more embodiments, and as illustrated in FIG. 15, light injected into a first edge 230 can be incident on a second edge 240 adjacent to the injection edge and a third edge 260 adjacent to the injection edge, wherein the second edge 240 is opposite the third edge 260. The second and third edges may also comprise a low average roughness Ra at the edge of less than 0.5 micrometers, 0.4 micrometers, 0.3 micrometers or 0.2 micrometers, measured by an optical profilometer, without etching with hydrofluoric acid and/or slurry polishing the edge so that the incident light undergoes total internal reflectance from the two edges adjacent the first edge.

Light may be injected into the first edge 230 from an array of LED's 300 positioned along the first edge 230. The LED's may be located a distance of less than 0.5 mm from the first edge 230. According to one or more embodiments, the LED's may have a thickness or height that is less than or equal to the thickness of the glass sheet to provide efficient light coupling to the light guide plate 200. According to one or more embodiments, the two edges 240, 260 may also comprise a diffusion angle in reflection that is less than 6.4 degrees.

Various modifications and variations can be made to the materials, methods, and articles described herein. Other aspects of the materials, methods, and articles described herein will be apparent from consideration of the specification and practice of the materials, methods, and articles disclosed herein. It is intended that the specification and examples be considered as exemplary. It will be apparent to those skilled in the art that various modifications and variations can be made without departing from the spirit or scope of the disclosure. 

1. An apparatus for finishing an edge of a glass sheet, the apparatus comprising: a worktable which supports the glass sheet while the edges are subjected to grinding and polishing, wherein an X-axis is a direction of lateral movement on a plane of a glass sheet on the worktable, a Y-axis is a direction of longitudinal movement on the plane which is perpendicular to the X-axis, and a Z-axis is a direction of orthogonal movement with respect to the plane; a first motor with a first spindle having a first spindle axis of rotation positioned on a first side of the plane, the first spindle axis aligned substantially along the X-axis; a second motor with a second spindle having a second spindle axis of rotation positioned on a second side of the plane, the second spindle axis aligned substantially along the X-axis; a first grinding wheel mounted on the first spindle, the first grinding wheel substantially disc-shaped with a peripheral edge to chamfer a first edge of the glass sheet using the peripheral edge of the first grinding wheel; and a second grinding wheel mounted on the second spindle, the second grinding wheel substantially disc-shaped with a peripheral edge to chamfer a second edge of the glass sheet using the peripheral edge of the second grinding wheel.
 2. The apparatus of claim 1, wherein one or more of the first spindle or the second spindle further comprises an additional grinding wheel.
 3. The apparatus of claim 1, wherein the first spindle and the second spindle are configured to create a chamfer of less than or equal to about 5% of a thickness of the glass sheet.
 4. The apparatus of claim 1, wherein each of the first grinding wheel and the second grinding wheel independently have an average particle size in the range of about 200 μm to about 3 μm.
 5. The apparatus of claim 1, wherein the first grinding wheel and the second grinding wheel are compliant urethane based wheels.
 6. The apparatus of claim 1, wherein the first spindle and the second spindle are spaced apart by greater than or equal to a radius of the first grinding wheel or second grinding wheel plus 10 mm.
 7. The apparatus of claim 1, wherein each of the first motor and the second motor are movable in the Z-axis a distance equal to or greater than 60 mm away from the worktable.
 8. The apparatus of claim 1, wherein the worktable is configured to move the glass sheet in a plane formed by the X-axis and Y-axis adjacent the first grinding wheel and the second grinding wheel.
 9. The apparatus of claim 8, wherein the worktable is configured to move the glass sheet at a rate in the range of about 5 m/min to about 30 m/min.
 10. The apparatus of claim 1, wherein each of the first grinding wheel and the second grinding wheel have a thickness sufficient to provide greater than or equal to about 25 mm of contact.
 11. The apparatus of claim 1, wherein the first motor and the second motor are pushed toward the worktable.
 12. The apparatus of claim 11, further comprising one or more of air bearings or force transducers coupled to the first motor and the second motor.
 13. The apparatus of claim 1, wherein the first motor and the second motor are configured to operate at a speed in the range of about 600 rpm to about 3000 rpm.
 14. The apparatus of claim 1, further comprising a plurality of first peripheral liquid cooling nozzles adjacent the first spindle and positioned to direct cooling liquid toward the peripheral edge of the first grinding wheel, and a plurality of second peripheral liquid cooling nozzles adjacent the second spindle and position to direct cooling liquid toward the peripheral edge of the second grinding wheel.
 15. The apparatus of claim 1, further comprising a plurality of remote liquid cooling nozzles positioned remotely from the first grinding wheel and the second grinding wheel and positioned to direct cooling liquid toward an edge of the glass sheet.
 16. A method of finishing an edge of a glass sheet, the method comprising: supporting a glass sheet on a worktable, a portion of the glass sheet extending a distance from the worktable, the glass sheet comprising a first surface, a second surface opposing the first surface and an end surface, the first surface and end surface intersect along a first edge and the second surface and the end surface intersect along a second edge, wherein an X-axis is a direction of lateral movement on a plane of a glass sheet on the surface, a Y-axis is a direction of longitudinal movement on the plane which is perpendicular to the X-axis, and a Z-axis is a direction of movement orthogonal to the plane; contacting the first edge with a peripheral edge of at least one first grinding wheel positioned on a first spindle axis of a first motor, the first grinding wheel substantially disc-shaped; contacting the second edge with a peripheral edge of at least one second grinding wheel positioned on a second spindle axis of a second motor, the second grinding wheel substantially disc-shaped; and producing relative motion between the first and second grinding wheels and the glass sheet during contacting of the first and second grinding wheels with the first and second edges, respectively, to chamfer the first edge and second edge.
 17. The method of claim 16, wherein the chamfer is less than or equal to about 5% of a thickness of the glass sheet.
 18. The method of claim 16, wherein the worktable is configured to move the glass sheet at a rate in the range of about 5 m/min to about 30 m/min.
 19. The method of claim 16, wherein each of the first grinding wheel and the second grinding wheel have a thickness sufficient to provide greater than or equal to about 25 mm of contact.
 20. The method of claim 16, further comprising providing a force to push the first motor and the second motor toward the worktable. 